Fuels distinguish one from the other with respect to their behavior as to volatility. Low volatile fuels having a low vapor pressure require an additional quantity of metered fuel especially as long as the engine has not yet reached its operating point. In some applications, the enrichment, which is needed for a cold start with low-volatile fuel compared to more volatile fuel, is up to 40%.
From U.S. Pat. No. 5,564,406, it is known to correct the fuel quantity to be injected in dependence upon the fuel quality. The fuel quality is derived from the behavior of the lambda control in the start phase.
A condition precedent for the adaptation of the fuel injection quantity in the known solution is therefore an operational ready lambda control. However, this is not immediately present at the start of the engine so that the detection of the fuel quality or the fuel characteristics is at least incomplete for some applications and primarily because the adaptation of the injection quantity is of special significance during the start phase. Furthermore, the fuel quality or the fuel characteristics are only indirectly detected so that statements as to the accuracy of the adaptation can be made only with difficulty.
For example, from U.S. Pat. No. 6,513,501, it is known to use a vapor filled fuel-pressure attenuator which is elastically deformable and which is utilized in a fuel distributor pipe of an internal combustion engine.
The method of the invention is for operating an internal combustion engine having a fuel distributor. The method includes the steps of: determining the pressure in the fuel distributor after the engine is shut off; and, determining a signal quantity for fuel metering to the engine in the next operating cycle thereof in dependence upon the pressure.
With the direct detection of the thermodynamic characteristics of the fuel, a precise, reliable and rapid determination of the fuel quality or the fuel characteristics is provided. This leads also to a satisfactory accuracy of the correction of the fuel injection quantity (here, injection quantity is understood hereinafter also to be the fuel mass which is to be injected).
It is of special advantage that the air/fuel ratio can be adjusted with greater accuracy so that the emission of toxic substances is reduced and the driving performance is improved. This advantage becomes especially evident in a cold start.
It is specially advantageous to measure the vapor pressure curve of the fuel during the shutoff phase in the fuel rail or fuel distributor with a pressure sensor in the metering pipe and to correct the injection quantity during the subsequent operating cycle of the engine in correspondence to this vapor pressure information. In an especially advantageous manner, the fuel quantity is therefore corrected also during the phases wherein it is still open-loop controlled and is not closed-loop controlled by means of a lambda control. This is especially important for the cold start and the warm up of the engine. Modern exhaust-gas requirements are therefore satisfied.
It is especially advantageous when the pressure sensor in the metering pipe is a pressure sensor which is utilized in the distributor pipe in the context of the electric control of the fuel pressure.